1. Field of the Invention
Embodiments of the present invention generally relate to pattern generation systems and methods used by such systems to form patterns on substrates, and more particularly, to an electron beam pattern generation system.
2. Description of the Related Art
Any effect on the exposure of a point in an imaged pattern by the exposure of any neighboring point may be called a proximity effect. For example, limited resolution of the electron optical exposure or inherent resist resolution, electron scattering in the resist layer and electron backscattering from the substrate on which the resist layer lies may cause a blurring of the exposure dose distribution delivered to a specific point. As a result, a portion of the exposure dose designed to be delivered to a specific point is in fact delivered to neighboring points. In addition, exposure of the resist layer at a specific point may result in localized heating of the resist that can diffuse outward to neighboring points. The result is modified resist sensitivity at those neighboring, proximate points. These effects may also be referred to as critical dimension effects.
Thermal expansion of the substrate on which the resist is formed is another localized heating effect that may result in feature placement errors at neighboring points through non-uniform thermal expansion of the substrate. These thermal expansion errors may also be referred to as placement effects.
In addition, during exposure by a charged particle beam, the resist may acquire a local charge. This charge may deflect the incoming particle beam, leading to pattern placement errors.
These proximity effects may result in an exposure dose error, real or effective, at specific points. Critical dimension effects and placement effects may cause real exposure dose errors by altering the location of the point where an electron influences the resist. Resist heating may result in an effective exposure dose error by altering the sensitivity of the resist to electrons.
Where critical dimension effects depend only on the total exposure dose delivered to neighboring sites, resist heating effects and placement effects may also be influenced by the rate and time sequence of exposure dose delivery. Thus, by a variety of mechanisms, proximity effects may result in unwanted variations in the size, shape and or location of lithographic features.
The correction of these errors is an important aspect of electron beam lithography, particularly in view of the trend to smaller geometries with increasingly complex patterns requiring greater precision and accuracy. A need, therefore, exists in the art for an improved method for minimizing, if not eliminating, critical dimension effects and placement effects in connection with generating a flash.